Certain aspects of the present invention relate to a wireless communication system for the purpose of expanding the region for transmitting data from a terminal. Several currently accepted standards exist to enhance wireless communication methods. Examples of these wireless communication methods between a base station device (hereinafter referred to as a base station BS (Base Station)) and a terminal device (hereinafter referred to as a terminal MS (Mobile Station)) are the wireless standards 802.16d (e.g., Non-Patent Document “IEEE Std 802.16TM-2004”) and 802.16e (e.g., Non-Patent Document “IEEE Std 802.16eTM-2005”).
FIG. 1 is an example of a service of the communication method by the wireless standards 802.16d or 16e. A single base station BS 100 is connected to a plurality of terminals MS 200-1 to 200-3. The communication method by 802.16d or 16e is based on a P-MP (Point-to-Multipoint) connection.
FIG. 14 is a configuration example of a frame in the 802.16d or 16e standard. The vertical axis indicates the frequency, and the horizontal axis indicates the time. Each frame includes a DL (Down Link) sub-frame and a UL (Up Link) sub-frame. Configuration information of the DL sub-frame and the UL sub-frame and information for communication control are described in a DL-MAP and a UL-MAP in the DL sub-frame. The terminal MS which has received the DL sub-frame from the base station BS performs reception processing and transmission processing by referring the DL-MAP and the UL-MAP.
Further, a Code Division Multiple Access (CDMA) region is set to the UL sub-frame. The terminal MS selects one of 256 code patterns called CDMA codes, then transmits the code to the base station BS in this region. The CDMA codes are categorized according to their purpose: Initial Ranging, Periodic Ranging, Bandwidth Request, and Handover Ranging. The 256 patterns of the CDMA codes can be divided into these four groups.
A position of this CDMA region is specified by a UL-MAP IE (Information Element) in the UL-MAP of the DL sub-frame. Further, a purpose of the CDMA region is specified by the UL-MAP IE at the same time. FIG. 15 is an example of the UL-MAP IE. The position of the CDMA region is specified by “OFDMA Symbol offset,” “Subchannel offset,” “No. OFDMA Symbols,” and “No. Subchannels.” That is, an offset from the start of the UL sub-frame to the start position of the CDMA region is specified by “OFDMA Symbol offset” in the time direction and “Subchannel offset” in the frequency direction. The number of symbols and subchannels in the CDMA region are specified by “No. OFDMA Symbols” in the time direction and “No. Subchannels” in the frequency direction, respectively.
Further, the purpose of the CDMA region is specified by a “Ranging Method.” If “00” or “01” is specified by the “Ranging Method,” the purpose of Initial Ranging and Handover Ranging are indicated. If “10” or “11” is specified, the purpose of Bandwidth Request and Periodic Ranging are indicated. For example, when the base station BS sets “00” as the “Ranging Method” and transmits the UL-MAP IE. If the terminal MS needs to perform the Initial Ranging, the terminal MS transmits the CDMA code indicating the Initial Ranging of the 256 patterns in the CDMA region of the UL sub-frame. Subsequently, the Initial Ranging is processed in the base station BS and the terminal MS.
In the wireless communication system, frequencies are assigned to each base station BS in view of interference, coverage, etc. FIG. 16 A is an example of the arrangement of the base stations, and FIG. 16 B is an example of frequency assignment. Each of frequency bands f1 to f3 is assigned to each of base stations, BS1 to BS3, respectively. Different frequency bands are used in neighboring base stations. In this case, since the frequency bands are divided into f1, f2 and f3, the frequency band that can be used in each base station is smaller than the total frequency (f1+f2+f3). However, since different frequencies are assigned to the neighboring base stations BS, interference is reduced and a wireless environment of the terminal MS existing at a cell edge is improved. Thus, more coverage can be secured than in the case that the same frequency is used in all the base stations.
One of the methods of frequency use in a wireless communication system based on the 802.16 d or 16e in WiMAX Forum (e.g., a non-patent document “Mobile WiMAX-Part I: A Technical Overview and Performance Evaluation (August, 2006)”) is Fractional Frequency Reuse (FFR). FIG. 17A is an example of the arrangement of the base stations, and FIG. 17B is an example of the frequency assignment by FFR.
As depicted in FIG. 17B, the frame of each base station BS is divided into two time regions (R1 Zone and R3 Zone) in FFR. In one Zone (R1 Zone), all the frequency bands (f1+f2+f3) are assigned. In the other Zone (R3 Zone), different frequencies are assigned in the neighboring base stations. In the R1 Zone, throughput can be improved because many frequency bands can be used. In the R3 Zone, coverage can be secured, so that the FFR can improve the throughput and the coverage.
FIG. 18A is an example of an arrangement of the base stations, and FIG. 18B is an example of the UL sub-frame. As shown in FIG. 18B, when different frequencies are assigned in the neighboring base stations, part of the frequencies assigned by each base station BS is used in the CDMA Region of the UL sub-frame (FIG. 14). On the other hand, in FFR case in the CDMA Region, part of the frequency assigned in each base station BS is used in the R3 Zone.
However, even though the CDMA region is a region that is used for such purposes as Ranging and Bandwidth-Request of the terminal MS, a problem occurs. The region for transmitting data of the terminal MS becomes smaller because part of the frequencies assigned to the base station BS is used. If the region for transmitting data is small, the amount of data that can be transmitted is reduced. Thus, various services may be disrupted.